Showing papers on "Maximum power point tracking published in 2007"

Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques

Abstract: The many different techniques for maximum power point tracking of photovoltaic (PV) arrays are discussed. The techniques are taken from the literature dating back to the earliest methods. It is shown that at least 19 distinct methods have been introduced in the literature, with many variations on implementation. This paper should serve as a convenient reference for future work in PV power generation.

A Single-Stage Grid Connected Inverter Topology for Solar PV Systems With Maximum Power Point Tracking

Abstract: This paper proposes a high performance, single-stage inverter topology for grid connected PV systems. The proposed configuration can not only boost the usually low photovoltaic (PV) array voltage, but can also convert the solar dc power into high quality ac power for feeding into the grid, while tracking the maximum power from the PV array. Total harmonic distortion of the current, fed into the grid, is restricted as per the IEEE-519 standard. The proposed topology has several desirable features such as better utilization of the PV array, higher efficiency, low cost and compact size. Further, due to the very nature of the proposed topology, the PV array appears as a floating source to the grid, thereby enhancing the overall safety of the system. A survey of the existing topologies, suitable for single-stage, grid connected PV applications, is carried out and a detailed comparison with the proposed topology is presented. A complete steady-state analysis, including the design procedure and expressions for peak device stresses, is included. Necessary condition on the modulation index "M" for sinusoidal pulsewidth modulated control of the proposed inverter topology has also been derived for discontinuous conduction mode operation. All the analytical, simulation and experimental results are presented.

Topology Study of Photovoltaic Interface for Maximum Power Point Tracking

Abstract: This paper looks at the performance of photovoltaic modules in nonideal conditions and proposes topologies to minimize the degradation of performance caused by these conditions. It is found that the peak power point of a module is significantly decreased due to only the slightest shading of the module, and that this effect is propagated through other nonshaded modules connected in series with the shaded one. Based on this result, two topologies for parallel module connections have been outlined. In addition, dc/dc converter technologies, which are necessary to the design, are compared by way of their dynamic models, frequency characteristics, and component cost. Out of this comparison, a recommendation has been made

Comparison of Traditional Inverters and $Z$ -Source Inverter for Fuel Cell Vehicles

Abstract: In this paper, three different inverters: conventional pulsewidth modulation (PWM) inverter, dc-dc boosted PWM inverter, and Z-source inverter were investigated and compared for fuel cell vehicle application. Total switching device power, passive components requirement, and constant power speed ratio of each of these inverters were calculated. For purposes of comparison, an example of the total switching device power, requirement of passive components, the constant power speed ratio, and the efficiencies of the different inverters for fuel cell vehicle powered by the same fuel cell were conducted. The comparisons show that the Z-source inverter is very promising in applications when the boost ratio is low (1-2).

Predictive & Adaptive MPPT Perturb and Observe Method

Abstract: The perturb and observe (P&O) best operation conditions are investigated in order to identify the edge efficiency performances of this most popular maximum power point tracking (MPPT) technique for photovoltaic (PV) applications. It is shown that P&O may guarantee top-level efficiency, provided that a proper predictive (by means of a parabolic interpolation of the last three operating points) and adaptive (based on the measure of the actual power) hill climbing strategy is adopted. The approach proposed is aimed at realizing, in addition to absolute best tracking performances, high robustness and promptness both in sunny and cloudy weather conditions. The power gain with respect to standard P&O technique is proved by means of simulation results and experimental measurements performed on a low power system. Besides the performance improvements, it is shown that the proposed approach allows possible reduction of hardware costs of analog-to-digital (A/D) converters used in the MPPT control circuitry.

Multi-Input Inverter for Grid-Connected Hybrid PV/Wind Power System

Abstract: The objective of this paper is to propose a novel multi-input inverter for the grid-connected hybrid photovoltaic (PV)/wind power system in order to simplify the power system and reduce the cost. The proposed multi-input inverter consists of a buck/buck-boost fused multi-input dc-dc converter and a full-bridge dc-ac inverter. The output power characteristics of the PV array and the wind turbine are introduced. The perturbation and observation method is used to accomplish the maximum power point tracking algorithm for input sources. The operational principle of the proposed multi-input inverter is explained. The control circuit is realized by using a digital signal processor and auxiliary analog circuits. For practical applications, functions of soft-start and circuit protection are implemented. Experimental results have shown the performance of the proposed multi-input inverter with desired features

A Single-Stage Three-Phase Grid-Connected Photovoltaic System With Modified MPPT Method and Reactive Power Compensation

Abstract: Single-stage grid-connected photovoltaic (PV) systems have advantages such as simple topology, high efficiency, etc. However, since all the control objectives such as the maximum power point tracking (MPPT), synchronization with the utility voltage, and harmonics reduction for output current need to be considered simultaneously, the complexity of the control scheme is much increased. This paper presents the implementation of a single-stage three-phase grid-connected PV system. In addition to realize the aforementioned control objectives, the proposed control can also remarkably improve the stability of the MPPT method with a modified incremental conductance MPPT method. The reactive power compensation for local load is also realized, so as to alleviate grid burden. A DSP is employed to implement the proposed MPPT controller and reactive power compensation unit. Simulation and experimental results show the high stability and high efficiency of this single-stage three-phase grid-connected PV system.

Comparison of the performance of maximum power point tracking schemes applied to single-stage grid-connected photovoltaic systems

Abstract: This work presents a comparison of various maximum power point tracking (MPPT) techniques applied to 1-Phi, single-stage, grid-connected photovoltaic (PV) systems. A representative single-stage grid-connected PV system, based on buck-boost converter topology operating in discontinuous current mode (DCM) with sine-triangle pulse width modulation (SPWM) and feeding sinusoidal power into the grid, is considered for this study. MPPT techniques are compared on the basis of the time taken to reach (track) the MPP, operating point oscillations in the vicinity of MPP and the dependence of the algorithms, if any, on array configuration and parameters. Comparison is also made on the basis of the energy extracted from the PV source during the transient tracking phase. In this context, an energy tracking factor term (E TF ) is introduced and defined. It is observed that all the MPPT schemes studied have their own merits and demerits. The ripple correlation and beta methods offer an overall good combination of desirable features. All the results of this study are presented.

Application of Z-Source Inverter for Traction Drive of Fuel Cell—Battery Hybrid Electric Vehicles

Abstract: This paper presents a Z-source inverter control strategy used to control power from the fuel cell, power to the motor, and state of charge (SOC) of the battery for fuel cell (FC)-battery hybrid electric vehicles (FCHEV). Traditional pulsewidth modulation inverter always requires an extra dc/dc converter to interface the battery in FCHEVs. The Z-source inverter utilizes an exclusive Z-source (LC) network to link the main inverter circuit to the FC (or any dc power source). By substituting one of the capacitors in the Z-source with a battery and controlling the shoot through duty ratio and modulation index independently, one is able to control the FC power, output power, and SOC of the battery at the same time. These facts make the Z-source inverter highly desirable for use in FCHEVs, as the cost and complexity is greatly reduced when compared to traditional inverters. These new concepts will be demonstrated by simulation and experimental results

Ground currents in single-phase transformerless photovoltaic systems

Abstract: The relative weight of the energy generated by means of renewable sources is constantly increasing. Among all these sources, the photovoltaic (PV) systems present the higher and more stable relative growth. However, the PV system is still too expensive and a significant effort is being done to increase the efficiency and reduce the cost. Concerning the PV inverters, this has lead to the elimination of the low frequency (LF) transformer that has been traditionally included. The LF transformer provides isolation from the grid but reduces the PV inverter efficiency and increases its size and cost. However, the elimination of the transformer might generate strong ground currents, which become now an important design parameter for the PV inverter. The ground currents are a function of the system stray elements. However, there is no simple model and procedure to study the common mode behavior of a PV system, which is required to analyze the ground currents. In this paper, a comprehensible model is proposed which provides a better understanding of the common mode issue in single-phase transformerless PV systems. In addition, a procedure is developed to analyze the global performance, efficiency, grid current quality, and common mode behavior of a PV inverter as a function of its particular structure and modulation technique. Copyright © 2007 John Wiley & Sons, Ltd.

Transformerless Photovoltaic Inverters Connected to the Grid

Abstract: Renewable energy sources are getting more and more widespread, mainly due to the fact that they generate energy by keeping the environment clean. Most of these systems have an isolation transformer included, which if excluded from the system would increase the efficiency and decrease the size of PV installations, furthermore it would lead to a lower cost for the whole investment. But there are some safety issues regarding the missing galvanic isolation. This paper is aiming to analyze and compare the most common single-stage transformerless PV inverter topologies for single-phase and three-phase with respect to the leakage current generation. The best results, both for single-phase and three-phase systems, are obtained when the middle point of the input capacitors is connected to the neutral point, thereby minimizing the voltage fluctuations present at the terminals of the PV panel.

Architecture Complexity and Energy Efficiency of Small Wind Turbines

Abstract: The power characteristics of wind turbines are nonlinear. It is particularly true for vertical-axis turbines whose provided power is very sensitive to the load. Thus, controlling the operating point is essential to optimize the energetic behavior. Several control strategies (maximum power point tracking) can be used for the energy conversion. If the wind-turbine characteristic Cp(lambda) is supposed to be a priori known, it can be used for optimal control of the torque, speed, or system output power. On the contrary, if this characteristic is unknown, an operational seeking algorithm such as fuzzy logic has to be implemented. Several structures with different associated complexity degrees can be used, in particular, the structure of the ac-dc conversion, which can be either a pulsewidth-modulation voltage-source rectifier or a simple diode bridge. A comparative study of the corresponding control strategies and architectures is proposed in this paper regarding the tradeoffs between structure complexity and energy efficiency. The analysis is based on simulations and experiments

Analytic Solution to the Photovoltaic Maximum Power Point Problem

Abstract: Photovoltaic (PV) power has been successfully used for over five decades. Whether in dc or ac form, photovoltaic cells provide power for systems in many applications on earth and space. Its principles of operation are therefore well understood, and circuit equivalents have been developed that accurately model the nonlinear relationship between the current and voltage of a photovoltaic cell. With the improved efficiencies of power electronics converters, it is now possible to operate photovoltaic system about its maximum power point (MPP) in order to improve the overall system efficiency. Hitherto, this problem has been tackled using tracking (MPPT) algorithms that iteratively find the point of maximum power and respond to changes in solar irradiance accordingly. A mathematical manipulation that uses the mean value theorem is presented here that provides the analytic solution of a point in a close neighborhood of the MPP. It is thoroughly proved that this point is enclosed in a ball of small radius that also contains the MPP and therefore can practically be considered as the MPP. Since the solution is analytic, no iterative schemes are necessary, and only a periodic measurement is required to adjust to changes in solar irradiance. A circuit is implemented that shows the validity of the theory and the accuracy of the solution.

Power transmission controller, power reception controller, non-contact point power transmission system, power transmitter, power receiver, and electronic apparatus

Abstract: PROBLEM TO BE SOLVED: To provide a power transmission controller, a power receiving controller or the like which can recharge a battery, while suppressing wasteful power consumption to minimum. SOLUTION: The power transmission controller provided to a power transmitter of a contactless power transmission system includes a power transmission side control circuit for controlling the power transmitter. When it is detected that a battery possessed by a load becomes fully charged, the power transmission side control circuit suspends normal power transmission to a power receiver to conduct intermittent power transmission. When it is detected that the battery becomes necessary for recharging during the intermittent power transmission period, the power transmission side control circuit performs the control reopening the normal power transmission to the power receiver. The power receiving side control circuit for controlling the power receiver performs the control transmitting to the power transmitter the recharging command notifying the information with regard to the recharging state of the battery, during the intermittent power transmission period. COPYRIGHT: (C)2008,JPO&INPIT

Performance Model for Grid-Connected Photovoltaic Inverters

Abstract: This document provides an empirically based performance model for grid-connected photovoltaic inverters used for system performance (energy) modeling and for continuous monitoring of inverter performance during system operation. The versatility and accuracy of the model were validated for a variety of both residential and commercial size inverters. Default parameters for the model can be obtained from manufacturers specification sheets, and the accuracy of the model can be further refined using measurements from either well-instrumented field measurements in operational systems or using detailed measurements from a recognized testing laboratory. An initial database of inverter performance parameters was developed based on measurements conducted at Sandia National Laboratories and at laboratories supporting the solar programs of the California Energy Commission.

Application of Centered Differentiation and Steepest Descent to Maximum Power Point Tracking

Abstract: This paper concentrates on two critical aspects to improve the performance of maximum power point tracking (MPPT). One improvement is to accurately locate the position of the maximum power point (MPP) by using the centered differentiation. Another effort is to reduce the oscillation around the MPP in steady state by controlling active perturbations. This paper also adopts the method of steepest descent for MPPT, which shows faster dynamic response and smoother steady state than the method of hill climbing. Comprehensive experimental evaluations have successfully illustrated the effectiveness of the proposed algorithm.

Method and system to provide a distributed local energy production system with high-voltage DC bus

Abstract: A method and system to provide a distributed local energy production system with high-voltage DC bus is disclosed. In one embodiment, a system comprises a management unit to be interconnected via a network bus to a set of link modules, each link module coupled to a separate local energy production unit, each link module to include a Maximum Power Point Tracking (MPPT) step-up converter and a parameter monitoring unit to produce parameter data for the respective local energy production unit, and the local energy production units to be coupled to a high voltage power line to deliver produced electrical energy to a consumer of the energy; and the management unit to receive measured parameters from the link modules, and to send control signals to link modules to provide individual operational control of the local energy production units, the management unit to be coupled to one or more separate computers to provide the computers with access to the parameter data and control of the local energy production units.

Unbalanced Grid Fault Ride-Through Control for a Wind Turbine Inverter

Abstract: Large variable speed wind turbines with fully rated, direct-in-line converters are increasingly used as silicon cost continues to decline. While grid codes require wind turbines to ride-through grid faults, including unbalanced faults, voltage source inverters interfaced to the grid are inherently sensitive to any unbalance in the a.c. voltage. This paper presents an unbalanced grid fault ride-through control method for such a wind turbine configuration. The method can be easily integrated into the power tracking control needed during normal operation. It is shown that the major constraint is the 2nd order harmonic to be absorbed by the d.c. link capacitor and that the control effectiveness depends on the voltage and current capabilities of the semiconductor devices in the inverter. Simulation and experimental results are used to validate the proposed control method and to identify the power limit that is necessary during ride-through.

A novel Parallel Active Filter for Current Pulsation Smoothing on single stage grid-connected AC-PV modules

Abstract: The newest technology on decentralised grid-connected PV systems is the "AC-PV Module", which is characterised by a number of clear advantages over conventional large PV systems. Single stage topologies seem to be a rather attractive solution, for these applications, since in generally they are characterised by high efficiency, low cost and simple structure with high reliability due to reduced components count. On the other hand in single-phase AC-PV Module inverters, the power that is transferred to the power network has a large amount of power pulsation at twice line frequency. So a large ripple of voltage and current appears at the PV module output. Taking into account that there is a close correspondence between the power that flows from a PV module and the point of operation, this fact leads to reduced PV power generation. In order to overcome this defect, this paper presents a novel current pulsation smoothing parallel active filter (CPS-PAF) which is independent from the inverter topology and his operation mode. Purpose of the proposed CPS-PAF is the elimination of the low frequency PV current ripple. So the PV module can be operated close enough to the maximum power point and consequently the PV generated electricity power is maximised. The CPS-PAF conception, control and effectiveness are validated by PSpice simulation and experimental results accomplished on a laboratory prototype.

A Control Method to Charge Series-Connected Ultraelectric Double-Layer Capacitors Suitable for Photovoltaic Generation Systems Combining MPPT Control Method

Abstract: A control method is described to charge series-connected ultraelectric double-layer capacitors (ultra-EDLCs) suitable for photovoltaic generation systems in combination with a maximum power point tracking (MPPT) control method. The EDLC charge control method allows the maximum power acquired by the MPPT control to be quickly charged into series-connected ultra-EDLCs no matter how the weather conditions may change. In the MPPT control, the output current of the solar arrays is controlled so that the output power converges on the maximum power in the prediction line previously determined based on the linearity between the maximum output power and the optimization current. The proportionality coefficient of the prediction line is automatically corrected using the hill-climbing method when the panel temperature of the solar arrays is changed. The EDLC charge control is performed with the three charge modes, i.e., the constant current charge mode, constant power charge mode, and the constant voltage charge mode while supervising the maximum voltage and allowable temperature of each series-connected EDLC. Effectiveness of the methods is verified by simulations and experiments

Maximum power point tracking using a fuzzy logic control scheme

Abstract: This paper proposes an intelligent control method for the maximum power point tracking (MPPT) of a photovoltaic system under variable temperature and insolation conditions. This method uses a fuzzy logic controller applied to a DC-DC converter device. The different steps of the design of this controller are presented together with its simulation. Results of this simulation are compared to those obtained by the perturbation and observation controller. They show that the fuzzy logic (...)

Leakage current evaluation of a singlephase transformerless PV inverter connected to the grid

Abstract: For low-power grid connected applications a single phase converter can be used. In PV applications it is possible to remove the transformer in the inverter in order to reduce losses, costs and size. Galvanic connection of the grid and the DC sources in transformerless systems can introduce additional leakage currents due to the earth parasitic capacitance. This currents increase conducted and radiated electromagnetic emissions, harmonics injected in the utility grid and losses. Amplitude and spectrum of leakage current depends on the converter topology, on the switching strategy and on the resonant circuit formed by the ground capacitance, the converter, the AC filter and the grid. In this paper, the leakage current in a 1.5 kW PV installation is measured under different conditions and used to build simulation model. The installation includes a string of sixteen PV panel, a full bridge inverter and a LCL filter. This model allows studying the influence of the harmonics injected by the inverter on the leakage current.

A Simple Single-Sensor MPPT Solution

Abstract: Maximum power point trackers (MPPTs) are used to ensure optimal utilization of solar cells. The implementation essentially involves sensing input current and voltage. An MPPT algorithm uses this information to maximize power drawn from the solar cells. Understandably, such realization is costly. Current state of the art allows replacing one of the sensors by complicated computations. In the present work, an empirical observation is used to develop a strategy, which employs a single voltage sensor and carries out simple computations for a buck converter-based MPPT